I am currently working on my thesis in Retrofitting of soft story. At first step i am trying to validate a experimental test. There i need to model a bracing with gap in it. The bracing should act only in compression after the gap is closed and free in tension. For creating simplified model i tried to create compression only element with uniaxial non linear elasticity model available for steel in Diana where i gave input to stress-strain diagram with very small value in tension and in compression, i gave nearly 0 value upto strain when gap closes and after that normal stress strain value of steel. I got the hysterisis result where there is increases in lateral resistance as compared to test result. how an i fix this? Is there any approach to model gap element? i tried contact analysis too but could not make it out.I have attached hysteresis result of Experiment and Diana Modeling. The bracing should start working after 1% drift.
Thank you.
It sounds like you are trying to model a bracing system with a gap that only acts in compression after the gap is closed and is free in tension. However, you are experiencing an increase in lateral resistance compared to the test results.
One approach you could consider is to use a gap element in your model. Gap elements are used to model a physical separation or a gap between two structural elements. They can be used to simulate the behavior of systems that experience large relative displacements, such as earthquake-induced structural vibrations. To implement a gap element, you can use a zero-length element that is inserted between the two parts of the bracing that will be separated by the gap. The stiffness of the element should be set to a very low value to represent the gap. Once the gap is closed, the stiffness of the element should increase to simulate the behavior of the bracing system.
Another approach you can consider is to adjust the stress-strain diagram you input into your model. It is possible that the values you have input for the steel's stress-strain diagram may not be appropriate for the specific steel used in the experiment. You could try to calibrate the stress-strain diagram by adjusting the parameters until the simulation results match the experimental results. This may involve adjusting the values for the elastic modulus, yield strength, and ultimate strength.
Lastly, you could also consider refining your contact analysis approach. This may involve adjusting the contact parameters, such as friction coefficients and contact stiffness, until the simulation results match the experimental results.
Could you provide the model geometry?
I worked in modeling the gap opening for self-centering shear wall using Diana software. May I can help you.
Add an interface element with your manual stiffness properties almost 0 till a certain displacement and then increase the stiffness when the gap is closed.
drop me an email if you need more info.
a.vandenbos_NLyseConsultants.com
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